Carrier communicating system



Feb. l, 1938. w. H. TlDD4 v2,107,168

CARRIER COMMUNICATING SYSTEM A TTORNEV Feb. l, 1938n w. H, TlDD CARRIERCOMMUNCATING SYSTEM Filed Feb. 12, 1936 2 Sheets-Shim?I 2 @Y Ok.

ATTORNEY Patented Feb. 1, 1938 UNITED STATES aromas PATENT OFFICECARRIER COMDIUNICA'IlNG SYSTEM Application February 12, 1936, Serial No.63,510

11 Claims.

This invention relates to an improved interconnecting and communicatingsystem, and more particularly to a system of the type in which carrierwaves or oscillations, either free or guided, 5 are employed as themedium for conveying energy for effecting the operation and control ofthe electrical switching, signaling and communicating apparatus locatedat separate points of the system. The invention especially relates to asystem in which carrier currents in the form of high frequency wavesguided upon wires are used as the medium of electrical connectionbetween the electrical devices and apparatuses located at differentpoints in the system. These carrier currents are assigned suchfrequencies that they are non-interfering with one another, so that eachcarrier serves as a connecting medium separate and distinct from theother carriers superposed upon the line or medium over which thecarriers are transmitted. Each of the carriers is modulated inaccordance with the voice currents or other signaling or controllingcurrents that are to be carried. The carriers thus modulated aretransmitted over the toll or long distance line or othercommon mediumsuch as, for instance, a pair of coaxial conductors and are passedthrough individual arrangements each of which is selective of onecarrier frequency to the exclusion of the others, and each of which :zumay have associated with it apparatus that serves to reproduce, from amodulated carrier, the voice,

signal or controlling currents with which the carrier was modulated atthe distant station.

The arrangement which is used to transmit and :'.3 receive by means ofany high frequency Wave as distinguished from that which is used totransmit and receive by means of a wave of a different frequency iscommonly known as a high frequency or carrier channel, or as a frequencyseo lective channel.

The present invention is directed particularly to a high frequencysystem in which intercommunication between the various stations of thesystem is effected through the medium of a numv ber of suchnon-interfering high frequency channels, each of which may be availableto all of the stations. Each of the stations of the system is soorganized that not only may it establish connection with any otherstation of the system by way of any of the high frequency channels. butit may also utilize, simultaneously, al1 of the channels that are not atthe time in use for the interconnection of other stations of the system.Furthermore, the system of the invention is so organized that eachstation has means for keeping at all times in operative relation withone or more of the channels available for outgoing calls and other meansfor immediately responding to a channel taken into use at a distantstation for a call directed to the incoming station, so that theinitiation of a call from a station finds an outlet or inlet for thecall at once available; and when one of the channels is taken into usefor an outgoing call, another is automatically preselected and placed inoperative relation with the means to be used for other and succeedingcalls. Further, when the channel bearing an incoming call has beenoperatively associated with an inlet through which the call is extendedto the wanted party, another inlet is immediately placed in a conditionto scan'the remaining channels for other and succeeding incoming calls.

In order to simplify the system, effect economy in the apparatusrequired andY realize certain advantageous features of operation, thesystem of the invention is further so organized that a number ofchannels, each comprising a pair of frequencies, are available to alloiices. However, the terminal equipment, that is, the outlet terminalsand inlet terminals, instead of having xed frequency filters, hasavailable variable frequency filters which can select any one of thesystem channels. The apparatus at each oflice consists of a plurality ofinward terminals and a plurality of outward terminals. These arearranged in such a manner that all outward terminals are automaticallyset on idle channels and one inward terminal is continuously scanningall the channels seeking a call for that particular oiiice. When achannel bearing such a call is found, responsive equipment causes thecall to be routed in any suitable manner to an idle position where it isproperly disposed of, while the scanning operations for other incomingcalls are, in the meanwhile, advanced to another idle inward terminal.

A clearer conception of the scope and purpose of the invention may beobtained from a consideration of the following description taken inconnection with the attached drawings in which Fig. 1 shows an outwardterminal connected to a common transmission medium such as, for example,a pair of coaxial conductors, together with cord connecting facilitiesfor extending a calling line to the terminal; while Fig. 2 shows aninward terminal connected o'n the one side to the same transmissionmedium as the outward terminal shown in Fig. 1 and, on

MD: and the demodulator DMn.

the other, to a call distribution cord-ended mechanism which functionsin the well-known manner to distribute the incoming calls among` anumber of inward positions for completion therefrom to the calledsubscribers. Inasmuch as call distribution terminal facilities are wellknown to the automatic telephone art, typical apparatus therefor is butschematically indicated in cooperation with the inward terminals,reference being made to such typical patents at Patv ent 1,861,754 to W.T. Powell issued on June '7,

1932 for a complete description of how such call distribution facilitiesoperate.

The equipment of the outward terminal shown in Fig. 1 includes, amongother elements, thc usual modulator MD1, oscillator CS1 and demodulatorDM1. Two variable frequency filters VF1 and VFz are connected betweenthe modulator MD1 and demodulator DM1 and the common medium CM. Thetuning of these filters and the tuning of the oscillator OS1 iscontrolledl simultaneously by a switch SW1, preferably of the rotarytype, having a magnet SWivwhich advances the brushes on the forwardstroke or the energization of the magnet to successive tuning points onthe corresponding terminal arcs of the switch. That is, a steppingcircuit is closed for switch magnet SW1 causing its operation to advancethe switch brushes one step to the apparatus of another carrier channel.If, now, the channel is idle, the apparatus is in readiness for usewhereas if the channel is busy, the busy carrier frequency will bedemodulated in the de- Jmodulator DM1 and the direct current whichresults from they demodulation process causes the operation of relay SR1which, through the bottom outer back contacts of relay PR, is bridgedacross the demodulator. Switch SW1 will then again be actuated toadvance its brushes to another channel.

Automatically tuned filters are, of course, not new. One type is shownin detail in the Patent 2,064,904, granted December 22, 1936, to E. I.Green, and the specific structure of circuit networks at the contacts ofrotary arcs for tuning the terminal to each of the different frequenciescan be used to serve a similar function in the present invention. Forthis reason such filters are only schematically indicated in thedrawings, reference' being made to the above-mentioned patent of E. I.Green for a detailed disclosure and description of their operation.

'I'he equipment of the inward terminal, shown in Fig. 2, includes theoscillator OS2, modulator These are connected through variable frequencyfilters VF: and VF1 to the common medium CM. The frequencies of responseof the filters VF: and VF4 and the oscillator frequency can be variedsimultaneously by means of the magnet MC which operates in the mannerdescribed hereinafter to attract therein one plate of a friction clutchto the periphery of a cooperating plate carried on a drive shaft gearedto the shaft of a motor-MO. When the two plates are in contact, theshaft which carries the filters VF: and VF1 rotates a number of rotarybrushes over corresponding arcs to tune the apparatus to the frequencyof an available channel, as in the case of the trunk or terminal shownin Fig. 1.

The inward terminals at each office operate successively, so that assoon as one terminal becomes busy, another starts hunting for incomingcalls. Thus only one of the sets of inward terwhich the incomingterminals in an office succeed each other in hunting for incoming calls,suppose that the terminal shown in Fig. 2 is to be energized next.Battery will b`e momentarily applied to conductor ST from a precedinginward terminal, or may be applied to start the system as a whole bydepressing the start key SK which also applies battery momentarily toconductor ST. 'Ihe connection of battery to conductor ST completes acircuit for relay AR which extends from grounded battery on saidconductor, bottom inner back contacts of relay ER, continuity vcontactsof relay AR and winding of relay AR, winding of clutch magnet MC toground. Relay AR operates and locks over its own upper front Acontactsto battery on the upper back contacts of relay BR, while magnet MCoperates and keeps operated through the locking circuit of relay AR. Themagnetic clutch disc is then attracted to the drive plate on the commonvertical drive shaft and causes the frequency of response of the filtersVFs and VF4 and the frequency of oscillator OS2 to be variedcontinuously and cyclically over the frequency range of the systemchannels.

Due to the variation in the tuning of the filter VF4, the demodulatorDMn receives, successively,

every frequency which is being transmitted over f the medium, and therelay CR will be actuated each time a. carrier is received, but this isof no consequence at this time. However, when a carrier is receivedwhich is modulated with the particular code frequency assigned to thisoffice, say,

frequency fa, this frequency, upon demodulation, will pass through thefilter or tuned circuit TC and be impressed upon the rectifier RE. 'I'herectifed current will, in turn, energize relay BR. The

operation of this relay, by breaking its upper back f contacts, willcause the deenergization of relay AR and that of magnet MC whichreleases, disconnects the driving plate of the clutch from the drivenplate and stopping filters VFa and VF1 and the oscillator OS2 onterminals which tune the response of said filters to frequency f1.Inasmuch as relay AR is slow-to-release, then, for a brief intervalduring which relay AR is in an operated position after it is unlocked, acircuit is completed from grounded battery on the upper front contactsof relay BR, lower contacts of relay AR, conductor ST2, the lower innerback contacts of relay ER of the next succeeding terminal and thence tothe corresponding circuit of relay AR and magnet MC of said terminal.This pulse starts the operation of the succeeding inward terminal whichnow takes up the call hunting function in the manner already described.

It is obvious that enough inward terminals should be provided to handlethe incoming peak traffic from all offices in order that there willalways be an idle terminal hunting for incoming calls. Should all theterminals become busy, the start pulse would not be received anywhereand the hunting sequence would stop. In this case it would be necessaryto press the start key SK as soon as there was an idle set of equipmentavailable.

I will now describe the establishment of a call between subscriber |00,whose line can be extended by any suitable means, such as cord C forinstance, to office A, and subscriber 200 who may be reached throughoffice B and any of the inward terminals thereof ending lin plug endedcords such as PL2 through the call distribution equipment CD.

In placing an outgoing call, the operator at office A first selects anidle outward terminal as will be indicated by the busy lamp BL beingdark. A plug PLi of a cord C having its other end plugged into thecalling subscriber's line |00 or the extension thereof, is inserted intothe jack JA. This connection completes a circuit for relay PR whichextends from ground through the cord supervisory lamp S, sleeve of theplug PLi and sleeve of the jack JA, winding of relay PR to groundedbattery. Relay PR operates and connects the power supply circuit PS tothe oscillator OS; and to the modulator MDi over its upper contacts,whereupon the carrier frequency to which the oscillator OSi andthemodulator MDi happen to be tuned by the setting of the brush arms ofVFi, is transmitted over the common medium. This, of course, makes thechannel busy, causing the relay SR1 in each ofthe other outwardterminals connected to the coinmon medium to operate and close thecircuit of the separate stepping switches SW1 to step the severalterminals off the contacts of the busy channel and onto an idle onewhere the oscillators and modulators are automatically adjusted to thefrequency of the idle channel as already described.

At the same time, the operation of relay PR opens the circuit of thestepping relay SR1 of the terminal taken into use, which circuitnormally extends over its lower outer back contacts, to prevent it fromoperating when the answering carrier is received. Over its lower outerfront contacts relay PR further completes the path of the relay RM sothat demodulated carrier current, when received as describedhereinafter, will operate said relay. Through its lower inner frontcontacts relay PR completes an obvious circuit for busy lamps such as BLwhich, upon lighting, indicate to the other positions that the terminalis busy.

The operator now depresses a key such as KYb in the code sending panelCS designating the called cnice B, which key remains mechanicallydepressed. This key permits a frequency fb, obtained from the oscillatorOSD, to be modulated on the carrier and transmitted to the common mediumthrough the operated contacts of key KY; of the cord C.' 'I'hefrequencies fc, fd, etc., correspond to the various other ofces in thesystem, there being apparatus at each of these offices to select theparticular frequency which identifies the office.

At the incoming olce B, the receipt of the incoming carrier modulated byfrequency fb assigned to this office, causes the operation of the relayBR in the incoming terminal which, at the moment, is performing the callhunting function and the operation of this relay causes a transfer ofthe call hunting function to the next incoming terminal in the series,as already described. Assuming that the incoming terminal shown in thedrawings is the terminal which responds to the carrier modulated byfrequency fb and that relay BR has operated in consequence, an obviouscircuit is now completed for relay DR which locks over its lowercontacts to battery on relay CR which is now operated by virtue of thepresence of the carrier upon the medium. 'I'he upper contacts Vof relayDR complete a circuit for the call lamp CL at an idle operators positionextending from grounded battery through the upper contacts of saidrelay,

bottom outer back contacts of relay ER, through the call distributionapparatus CD which is operated in the well-known manner to advance thepath of this circuit to an idle operators position, lamp CL at saidposition to ground. The call distributor apparatus CD functions in sucha manner that the calls received by the various inward terminals aredistributed among a number of operators positions. At each of thesepositions are a number of circuits from the call distributor, eachterminated in a plug such as PL2 and having associated therewithsupervisory and call lamps such as lamps SL and CL.

When a call lamp such as CL is lightedfat the associated position, theoperator thereat connects her circuit OS by means of KYg to theparticular cord to which the incoming call has been connected by thecall distributor. This key, at the same time, connects ground over anassociated circuit through the call distributor to operate relay ER.This relay, over its top outer contacts, connects power supply PS1 tothe oscillator OS2 and to modulator MD2 for producing and transmittingthe outgoing carrier. Over its top inner contacts it connects the ordertone circuit OT to the line by means of which a voice frequency iscaused to modulate the outgoing carrier. The order tone circuit may beof a wellknown type such, for example, as is disclosed in Patent1,719,494 granted July 2, 1929 to H. W. t

Ulrich and W. B. Prince, which when started applies two zips of tonecurrent to the circuit with which it is associated and then removes thetone current for the duration of the connection.

This modulated carrier is received at the originating office by thedemodulator DMi which operates magnet RM to mechanically restore key KYband cut off the code frequency fb from the oscillator OSb.

Further, upon receipt of the order tone from the wanted oflice B, thesubscribers number is passed to said office and the connection iscompleted so far as the outward terminal is concerned.

At office B, the operation of relay ER as a1- ready described, furthercauses the transfer of the start pulse circuit to the next incomingterminal for the duration ofl the call by the fact that the conductor STis now transferred over its bottom inner front contacts to conductor ST2which extends to the bottom inner back contacts of relay ER of thesucceeding terminal and thence to the winding of relay AR of thatterminal. At its outer lower back contacts, relay ER furtherextinguishes the call lamp CL and transfers the lighting circuit to thesupervisory lamp SL.

The operator now completes the call by insorting the plug PL2 into thejack of the subscribers line 20B. and key KY2 is released, relay ER isheld operated by means of ground on the sleeve contact of thesubscribers line jack. The operator can now proceed with the completionof another call.

When the connection is completed and a signal to that effect is given inthe well-known manner to the originating operator, she removes her plugPLi from jack JA, whereupon relay PR releases, the oscillator CS1 andmodulator MDi are removed from the line and the carrier is removed fromthe medium. This causes the deenergization of relay CR at the incomingterminal which, in turn. unlocks relay DR causing it to release,whereupon the circuit of the supervisory lamp SL is opened and this lampis extinguished,

When thisis accomplished thereby informing the inward operator that thecall is completed. Plug PL2 is then removed from the subscribers jack.This operation causes the release of relay ER and leaves the apparatusidle and ready to start hunting for an incoming call upon receipt of astart pulse over conductor ST.

What is claimed is:

1. In a high frequency communicating system, a calling station and acalled station, a plurality of high frequency carrier channels common tosaid stations, means at said calling station for maintaining an idle oneof said carrier channels preselected for use on a subsequent outgoingcall, and means at said called station for identifying the channelpreselected.

2. In a carrier communicating system provided with a number of carrierfrequency communicating channels, the combination with a commontransmission medium, of an outgoing terminal connected to said mediumcomprising a variable frequency oscillator to produce each of saidcarrier frequencies, a pair of variable frequency filters to pass eachof said carrier frequencies, a modulator for varying the outgoingcarrier, a demodulator capable of responding to each of said carrierfrequencies, a relay bridged across said demodulator when said terminalis not in use and operative by demodulated carrier currents, and meansresponsive to said relay for tuning said oscillator to produce andtuning said filters to pass a carrier frequency different from thecarrier frequency that caused said relay to operate.

3. In a carrier communicating system provided with a number of carrierfrequency communicating channels, the combination with a commontransmission medium of an incoming terminal connected to said mediumcomprising a variable frequency oscillator to produce each of saidcarrier frequencies, a pair of variable frequency filters to pass eachof said carrier frequencies, a modulator for varying the outgoingcarrier, a demodulator capable of responding to each of said carrierfrequencies, means responsive to an operation in said terminal fortuning said oscillator and said filters in succession to each of thecarrier frequencies, a tuned circuit connected in series with saiddemodulator and responsive to a specific modulation of any carrierfrequency, and means responsive to said specific modulated current forcausing the tuning of said oscillator and said filters to remain at thetuning point of the carrier frequency specifically modulated. I

4. In a carrier communication system provided with a number of differenthigh frequency carrier channels, an office comprising a plurality ofoutward terminals each provided with a carrier frequency current source,a plurality of inward terminals, means in each of said outward terminalsfor automatically varying the frequency of said carrier frequency sourceto the frequencies of different carrier channels to preselect an idlecarrier channel for use on a subsequent outgoing call, and means forsetting one of said inward terminals to continuously scan all vof saidcarrier channels for an incoming call for said office over one of saidchannels.

5. In a carrier communicating system pro-l vided with a number ofdifferent high frequency carrier channels, an office comprising aplurality of outward terminals each provided with a carrier frequencycurrent source, a plurality of inward terminals, means in each of saidoutward terminals for automatically varying the frequency of saidcarrier frequency source to the frequencies of different carrierchannels to preselect an idle carrier channel for use on a subsequentoutgoing call, means for setting one of said inward terminals tocontinuously scan all of said carrier channels for an incoming call tosaid office over one of said channels, a plurality of operatorspositions, call distribution facilitates interconnecting said inwardterminals with said operators positions, and means in said calldistribution facilities responsive to an inward terminal responding to acarrier channel appropriated for an incoming call for routing saidterminal to an idle operators position.

6. In a carrier communicating system provided with a number of differenthigh frequency carrier channels, an office comprising a plurality ofoutward terminals each provided with a carrier frequency current source,a plurality of outward terminals, means in each outward terminal forautomatically varying the frequency of said carrier frequency source tofrequencies of different carrier channels to preselect an idle carrierchannel for use on a subsequent outgoing call,`

means for setting one of said inward terminals to continuously scan allof said carriergchannels for an incoming call for said oilice over oneof said channels, and means responsive to an inward terminal connectingwith a channel carrying an incoming call for advancing the scanningfunction to another inward terminal.

'1. In a carrier communicating system provided with a number ofdifferent high frequency carrier channels, an office comprising aplurality of outward terminals each provided with a carrier' frequencycurrent source, means for automatically varying the frequency of thecarrier frequency source of each outward terminal to a frequency not inuse on any carrier channel, and means responsive to the appropriation ofan idle carrier channel by one of said outward terminals for changingthe frequency of the carrier current sources of all other terminals to afrequency not in use on any of said channels.

8. In a carrier communicating system provided with a number of carrierfrequency communicating channels, the combination with a commontransmission medium of means for modulating any one of said carrierfrequencies with any one of a plurality of calling frequencies, anincoming terminal connected to said medium comprising a lter variable topass each of said carrier frequencies, a demodulator responsive to eachof said carrier frequencies, a vfilter bridged across said demodulatorand tuned to be responsive to a particular one of said callingfrequencies, a relay responsive to the passage of said calling frequencythrough said tuned filter, means for continuously varying said variablefilter to scan all of said carrier channels, and means effective uponthe operation of said relay for arresting the variation of said variablefilter in a position to maintain said terminal tuned to the carrierfrequency so modulated.

9. In a carrier communicating system provided with a number of carrierfrequency communicating channels, the combination with a commontransmission medium of means for modulating any one of said carrierfrequencies with any one of a plurality of calling frequencies, anincoming terminal connected to said medium comprising a filter variableto pass each of said carrier frequencies, a demodulator responsive toeach of said carrier frequencies, a filter bridged across saiddemodulator and tuned to be responsive to a particular one of saidcalling frequencies, a relay responsive to the passage of said callingfrequency through said tuned filter, means for continuously varyingsaidvariablelter to scan all of said carrier channels, means effectiveupon the operation of said relay for arresting the variation of saidvariable filter in a position to maintain said terminal tuned to thecarrier frequency so modulated, and a signal controlled by said relayfor indicating an incoming call.

10. In a carrier communicating system provided with a number of carrierfrequency communicating channels, the combination with a common mediumof means for temporarily modulating any one of said carrier frequencieswith any one of a plurality of calling frequencies, an incoming terminalconnected to said medium comprising a filter variable to pass each ofsaid carrier frequencies, a demodulator responsive to each-of saidcarrier frequencies, a relay bridged across said demodulator andresponsive upon the demodulation of any one of said carrier frequencies,a filter bridged across said demodulator and tuned to be responsive to aparticular one of said calling frequencies, a second relay responsive tothe passage of said calling frequency through said tuned filter, meansfor continuously varying said variable filter to scan all of saidcarrier channels, means effective upon the operation of said secondrelay for arresting the variation of said variable filter in a positionto maintain said terminal tuned to the carrieri frequency so modulated,a signal controlled by said second relay for indicating an incomingcall, and means controlled by said first relay for maintaining saidsignal operated following the' withdrawal of said calling frequency.

11. In a carrier communicating system provided with a number of carrierfrequency communicating channels, the combination with a common mediumof means for modulating any one of said carrier frequencies with any oneof aplurality of calling frequencies, a plurality of incoming terminalsconnected to said medi- -um each comprising a lter variable to pass eachof said carrier frequencies, a demodulator responsive to each of saidcarrier frequencies, a

filter bridged across said demodulator and tuned to be responsive to aparticular one of said calling frequencies, a relay responsive to thepassage of said calling frequency through said tuned filter, meansoperative when said incoming terminal is idle for continuously varyingsaid variable filter to scan' all of said carrier channels, meanseffective upon the operation of said relay for arresting the variationof said variable filter in a position to maintain said terminal tuned tothe carrier frequency so modulated, and means responsive to said lastmeans for starting the variation of the variable filter of the nextidle`

